Methods for production of 1,2,4-triazol-3-one

ABSTRACT

Novel methods for producing 1,2,4-triazol-3-one from semicarbazide hydrochloride and formic acid are provided. In methods of this invention, ethanol is used in removal of unreacted formic acid to increase yield and purity of produced 1,2,4-triazol-3-one.

BACKGROUND

1,2,4-triazol-3-one is useful as a raw material for production ofnitro-1,2,4-triazol-3-one [(NTO) (C₂H₂N₄O₂)], a known explosive withhigh energy and low sensitivity. NTO is widely used in explosiveformulations and gas generators for automobile inflatable airbagsystems.

It would be beneficial to the defense industry and to the automobileairbag industry if there were methods for production of1,2,4-triazol-3-one that provided commercially acceptable yield andproduct purity.

THE INVENTION

This invention meets the above-described needs by providing novelmethods for production of 1,2,4-triazol-3-one. Methods according to thisinvention can produce 1,2,4-triazol-3-one having a purity of at leastabout 98.5% at yields of up to about 76%.

Methods of this invention can comprise (i) combining semicarbazidehydrochloride and formic acid to form an initial composition, optionallyin amounts such that the formic acid is combined in up to about 7equivalents as to the semicarbazide hydrochloride, (ii) heating theinitial composition to a temperature of about 70° C. to about 105° C.and maintaining the temperature for at least about 1 hour to form aproduct composition, (iii) distilling the product composition to removeat least a portion of unreacted formic acid and form a concentratedproduct composition, optionally recovering at least a portion of theremoved unreacted formic acid for use in (i), (iv) combining theconcentrated product composition and ethanol and, optionally, heating toat least about 40° C., optionally over a period of at least about 10minutes, (v) cooling the concentrated product composition to at leastabout 20° C., (vi) collecting crude 1,2,4-triazol-3-one from theconcentrated crude product composition, combining with water, andheating to a crystallization temperature high enough to dissolve crude1,2,4-triazol-3-one, e.g., at least about 70° C., to form a productsolution, (vii) cooling the product solution to lower than about 10° C.,optionally over a period of at least about 2.5 hours, and (viii)collecting recrystallized 1,2,4-triazol-3-one from the product solution.The recrystallized 1,2,4-triazol-3-one can be dried, e.g., under vacuumat an appropriate temperature, e.g., 40° C.

FIGURES

The invention will be better understood by reference to the FIGURE (FIG.1), which illustrates the solubility of 1,2,4-triazol-3-one in water andin formic acid.

DESCRIPTION

Various means for heating, cooling, maintaining temperatures,distilling, recovering distilled unreacted formic acid, and collectingproduced product are known to those skilled in the art. This inventionis not limited to the means described in the description and exampleprovided herein.

According to methods of this invention, semicarbazide hydrochloride canbe reacted with formic acid to produce the 1,2,4-triazol-3-one. Thesemicarbazide hydrochloride and the formic acid can be combined inamounts such that the amount of formic acid is only up to about 7 molarequivalents as to the semicarbazide hydrochloride. The semicarbazidehydrochloride and formic acid initial composition can be heated to atemperature of at least about 70° C., e.g., about 95° C. to about 105°C., and maintained at the temperature for at least about 1 hour toproduce crude 1,2,4-triazol-3-one. While the reaction is typicallyconducted at atmospheric pressure, greater than atmospheric pressure maybe employed if desired. The reaction time can vary up to several hoursor more, depending upon the amounts of formic acid and semicarbazidehydrochloride combined.

After the desired reaction time, the product composition that was formedcan be cooled to about 50° C. to about 40° C. Cooling can beaccomplished by direct cooling or by evaporative cooling, e.g., undervacuum. After the desired reaction time or after cooling, the productcomposition can be distilled to remove at least a portion of unreactedformic acid; some water can also be removed during the distillation. Asdesired, at least a portion of the unreacted formic acid can berecovered for use in reacting with semicarbazide hydrochloride. Theconcentrated product composition can be slurried in ethanol and, ifdesired, the slurry can be heated to at least about 40° C., over aperiod of at least about 10 minutes, or for as long as is needed todissolve any remaining unreacted formic acid in the concentrated productcomposition. If heated, the slurry can then be cooled to at least about20° C. Crude 1,2,4-triazol-3-one can be collected from the concentratedproduct composition.

The crude 1,2,4-triazol-3-one can be recrystallized by adding (combiningwith) water to form a crude solution and heating the crude solution toat least about 70° C. to about 100° C. to dissolve the solids, followedby cooling. Use of water as the recrystallization solvent assists withremoval of chlorides from the distilled product. Produced solid1,2,4-triazol-3-one can be collected on a filter, washed, e.g., withwater, and dried under vacuum at an appropriate temperature, e.g., 40°C., or other appropriate temperature. The ratio of recrystallizationsolvent, i.e., water, to product mass (isolated dried solid1,2,4-triazol-3-one) can be as low as 1.75.

Methods of this invention are particularly advantageous in that theyallow for removal of unreacted formic acid from the product compositionand the concentrated product composition. Refer to the FIGURE (FIG. 1),which illustrates that 1,2,4-triazol-3-one is much more soluble informic acid than it is in water. Thus removal of unreacted formic acidleads to a higher yield of the desired product, 1,2,4-triazol-3-one,than would otherwise be achieved. The FIGURE also illustrates that thedifference in solubility between water and formic acid is greater atlower temperatures. The FIGURE also shows a single data point forsolubility of the product in ethanol, i.e., 6% solubility at 76° C.,which is much lower than the solubility in either water or formic acid.The purpose of the ethanol slurry is to dissolve away the remainingformic acid and water, while forcing the 1,2,4-triazol-3-one product outof solution by using a solvent (ethanol) in which it has very lowsolubility. The solubility in water as shown in the FIGURE shows theadvantage of recrystallizing in water (with as little formic acid aspossible), as described herein.

The following example is illustrative of the principles of thisinvention. It is understood that this invention is not limited to anyone specific embodiment exemplified herein, whether in the example orthe remainder of this patent application.

EXAMPLE

Semicarbazide hydrochloride (142 g., 1.27 mol) and 96% formic acid (0.40kg, 8.7 mol) were added to a 1-L 4-neck RB flask with mechanicalstirrer, condenser, thermocouple, and caustic scrubber attached. Thereaction was heated to 105° C. for 1 hour. During the heating (startingat about 70° C.) there was considerable HCl gas evolution into thescrubber. After cooling to 45-50° C., the bulk of the formic acid (andwater byproduct) was distilled off on a rotovap with a 40° C. bath at25-35 mm vacuum. The white slurry was taken up in ethanol (50 mL),heated to 40° C. for 10 minutes, and cooled to 20° C. Crude product wascollected on a sintered glass funnel and washed with ethanol (30 mL).The crude product and water (150 mL) were heated to 95° C. to dissolvethe solids and cooled to 5° C. over 2.5 hours. The recrystallizedproduct was collected in a filter, washed with water (30 mL), and driedat 40° C. under high vacuum, affording 78.9 g (72%) of a white,crystalline solid (quant NMR=98.6%).

It is to be understood that the reactants and components referred to bychemical name or formula anywhere in the specification or claims hereof,whether referred to in the singular or plural, are identified as theyexist prior to being combined with or coming into contact with anothersubstance referred to by chemical name or chemical type (e.g., anotherreactant, a solvent, or etc.). It matters not what chemical changes,transformations and/or reactions, if any, take place in the resultingcombination or solution or reaction medium as such changes,transformations and/or reactions are the natural result of bringing thespecified reactants and/or components together under the conditionscalled for pursuant to this disclosure. Thus the reactants andcomponents are identified as ingredients to be brought together inconnection with performing a desired chemical reaction or in forming acombination to be used in conducting a desired reaction. Accordingly,even though the claims hereinafter may refer to substances, componentsand/or ingredients in the present tense (“comprises”, “is”, etc.), thereference is to the substance, component or ingredient as it existed atthe time just before it was first contacted, combined, blended or mixedwith one or more other substances, components and/or ingredients inaccordance with the present disclosure. Whatever transformations, ifany, which occur in situ as a reaction is conducted is what the claim isintended to cover. Thus the fact that a substance, component oringredient may have lost its original identity through a chemicalreaction or transformation during the course of contacting, combining,blending or mixing operations, if conducted in accordance with thisdisclosure and with the application of common sense and the ordinaryskill of a chemist, is thus wholly immaterial for an accurateunderstanding and appreciation of the true meaning and substance of thisdisclosure and the claims thereof. As will be familiar to those skilledin the art, the terms “combined”, “combining”, and the like as usedherein mean that the components that are “combined” or that one is“combining” are put into a container with each other. Likewise a“combination” of components means the components having been puttogether in a container.

While the present invention has been described in terms of one or morepreferred embodiments, it is to be understood that other modificationsmay be made without departing from the scope of the invention, which isset forth in the claims below.

1. A method for producing 1,2,4-triazol-3-one comprising (i) combiningsemicarbazide hydrochloride and formic acid to form an initialcomposition, (ii) heating the initial composition to a temperature of atleast about 70° C. and maintaining the temperature for at least about 1hour to form a product composition, (iii) distilling the productcomposition to remove at least a portion of unreacted formic acid andform a concentrated product composition, (iv) combining the concentratedproduct composition and ethanol, (v) collecting crude1,2,4-triazol-3-one from the concentrated crude product composition andethanol combination, (vi) combining the crude 1,2,4-triazol-3-one withwater and heating to a crystallization temperature high enough todissolve crude 1,2,4-triazol-3-one to form a product solution, (vii)cooling the product solution to lower than about 10° C., and (viii)collecting recrystallized 1,2,4-triazol-3-one from the product solution.2. The method of claim 1 wherein the formic acid is combined in up toabout 7 equivalents as to the semicarbazide hydrochloride.
 3. The methodof claim 1 wherein the cooling is conducted over a period of at leastabout 2.5 hours.
 4. The method of claim 1 further comprising (ix) dryingthe recrystallized 1,2,4-triazol-3-one under vacuum.
 5. A method forproducing 1,2,4-triazol-3-one comprising (i) combining semicarbazidehydrochloride and formic acid to form an initial composition in amountssuch that the formic acid is combined in up to about 7 equivalents as tothe semicarbazide hydrochloride, (ii) heating the initial composition toa temperature of at least about 70° C. and maintaining the temperaturefor at least about 1 hour to form a product composition, (iii)distilling the product composition to remove at least a portion ofunreacted formic acid and form a concentrated product composition, (iv)combining the concentrated product composition and ethanol, (v)collecting crude 1,2,4-triazol-3-one from the concentrated crude productcomposition, (vi) combining the crude 1,2,4-triazol-3-one with water,and heating to at least about 70° C. to form a product solution, (vii)cooling the product solution to lower than about 10° C. over a period ofat least about 2.5 hours, (viii) collecting recrystallized1,2,4-triazol-3-one from the product solution; and (ix) drying therecrystallized 1,2,4-triazol-3-one.